Dmitry Peskov, spokesman for Russian President Vladimir Putin, called it "an act of aggression against a sovereign nation".

The attack, at 04:40 Syrian time (01:40 GMT), comes just days after dozens of civilians, including many children, died in the suspected nerve gas attack in the town of Khan Sheikhoun in Idlib province.

Speaking from his Mar-a-Lago estate in Florida, Mr Trump branded President Assad a "dictator" who had "launched a horrible chemical weapons attack on innocent civilians".

Mr Trump said he had acted in America's "vital national security interest" to prevent the use of chemical weapons.

"Tonight I call on all civilised nations to join us in seeking to end this slaughter and bloodshed in Syria and also to end terrorism of all kinds and all types," he said.

The UK government called the US strike "an appropriate response to the barbaric chemical weapons attack".

The Pentagon said the Russian military, which supports Syrian government forces, had been informed ahead of the US action.

In a statement the Pentagon said missiles fired from Navy destroyers USS Porter and USS Ross had targeted aircraft, aircraft shelters, storage areas, ammunition supply bunkers, air defence systems, and radars at Shayrat airfield in western Homs province.

The Pentagon added that the strike was intended "to deter the regime from using chemical weapons again".

A Russian defence ministry statement read on state television said the US attack had been “ineffective” and claimed Syrian authorities were looking for 36 Tomahawk missiles which fell outside the base and missed the target.

The statement also confirmed that Russia would stop cooperation and communication with US forces in Syria.

The Russian state news reporter Evgeny Poddubny is at the base and posted a video of the damage on his instagram account. He also wrote that his “preliminary information” at the base is that nine jets were destroyed in the strike.

Air strikes may have struck the Syrian town of Khan Sheikhoun on Friday, where a chemical attack killed scores of people this week, according to a witness in the rebel-held area and a war monitoring group, the Syrian Observatory on Human Rights (SOHR).

Iran, Assad’s staunch regional backer, was quick to condemn the US strike on Syria’s al-Shayrat airfield, saying it violated international law and risks complicating the conflict to a new level.

Tehran authorities also questioned claims that Assad was behind the chemical attack on Khan Sheikhun.

“The Islamic Republic of Iran, as the biggest victim of chemical weapons in the contemporary history, condemns all uses of chemical weapons regardless of their users or victims, and at the same time, considers any unilateral measure with this excuse as dangerous, destructive, and violating of the imperative principles of the international law,” said Bahram Ghasemi, Tehran’s foreign ministry spokesman, according to the semi-official Mehr news agency.

“We believe that the American missile attack on Shayrat air base in Syria launched from US warships, with the excuse of the mysterious chemical attack on Khan Shaykhun, Idlib, whose time, executers, and beneficiaries are shrouded in mystery, strengthens the near-to-death terrorists and complicates the situation in Syria and the whole region,” he added.

Russia 24 TV has shown images of damage at the Shayrat airbase targeted by the US airstrike. Here are some screengrabs shown on BBC News:

The Russian foreign minister, Sergei Lavrov, who is in Tashkent today, said it appears there were no Russian servicemen killed in the missile strikes.

He also compared the action to the 2003 invasion of Iraq but said “at least that time they tried to bring some evidence forward”.

Other politicians in Russia are lining up to condemn the US airstrike, with many claiming the news of the chemical attack was a “fake” in order to provide a pretext for military action.

Hillary Clinton called for the US to take out Syrian government-controlled airfields just hours before Donald Trump launched airstrikes against Bashar al-Assad’s regime, PA reports.

Speaking in her first public interview since losing the US election in November last year, Clinton said Assad’s aerial power had been the key component behind widespread civilian deaths since the start of the civil war in 2011.

President Trump authorised the launchof cruise missiles in the early hours of Friday morning on a Syrian airbase thought to be behind this week’s chemical weapons attack.

Speaking to the New York Times columnist Nicholas Kristof, Clinton said she believed the US had been wrong not to have previously launched such an offensive.

She said: “Assad had an air force, and that air force is the cause of most of the civilian deaths, as we have seen over the years and as we saw again in the last few days.

“And I really believe that we should have and still should take out his airfields and prevent him from being able to use them to bomb innocent people and drop Sarin gas on them.”

Angelino Alfano, the Italian foreign minister, said in a statement that Italy understood the reasons behind US military action and called the strikes a “proportionate” deterrent to the further use of chemical weapons by the Assad regime.

Alfano called for a “necessary and urgent” meeting of the UN security council – where Italy, a non-permanent member, currently has a vote – and the adoption of a consensus resolution to prevent further atrocities.

He also pointed to Rex Tillerson’s upcoming visit to Moscow, suggesting that the US secretary of state could encourage Russia to use its influence in Syria and with Assad to agree “a real ceasefire, full humanitarian access and a gradual building of trust between the Syrian parties”.

1 new update

15m ago 10:49

A Russian defence ministry statement read on state television said the US attack had been “ineffective” and claimed Syrian authorities were looking for 36 Tomahawk missiles which fell outside the base and missed the target.

The statement also confirmed that Russia would stop cooperation and communication with US forces in Syria.

The Russian state news reporter Evgeny Poddubny is at the base and posted a video of the damage on his instagram account. He also wrote that his “preliminary information” at the base is that nine jets were destroyed in the strike.

Air strikes may have struck the Syrian town of Khan Sheikhoun on Friday, where a chemical attack killed scores of people this week, according to a witness in the rebel-held area and a war monitoring group, the Syrian Observatory on Human Rights (SOHR).

19m ago 10:45

Iran, Assad’s staunch regional backer, was quick to condemn the US strike on Syria’s al-Shayrat airfield, saying it violated international law and risks complicating the conflict to a new level.

Tehran authorities also questioned claims that Assad was behind the chemical attack on Khan Sheikhun.

“The Islamic Republic of Iran, as the biggest victim of chemical weapons in the contemporary history, condemns all uses of chemical weapons regardless of their users or victims, and at the same time, considers any unilateral measure with this excuse as dangerous, destructive, and violating of the imperative principles of the international law,” said Bahram Ghasemi, Tehran’s foreign ministry spokesman, according to the semi-official Mehr news agency.

“We believe that the American missile attack on Shayrat air base in Syria launched from US warships, with the excuse of the mysterious chemical attack on Khan Shaykhun, Idlib, whose time, executers, and beneficiaries are shrouded in mystery, strengthens the near-to-death terrorists and complicates the situation in Syria and the whole region,” he added.

25m ago 10:39

Russia 24 TV has shown images of damage at the Shayrat airbase targeted by the US airstrike. Here are some screengrabs shown on BBC News:

The Russian foreign minister, Sergei Lavrov, who is in Tashkent today, said it appears there were no Russian servicemen killed in the missile strikes.

He also compared the action to the 2003 invasion of Iraq but said “at least that time they tried to bring some evidence forward”.

Other politicians in Russia are lining up to condemn the US airstrike, with many claiming the news of the chemical attack was a “fake” in order to provide a pretext for military action.

Updated at 10.56am BST

39m ago 10:25

Hillary Clinton called for the US to take out Syrian government-controlled airfields just hours before Donald Trump launched airstrikes against Bashar al-Assad’s regime, PA reports.

Speaking in her first public interview since losing the US election in November last year, Clinton said Assad’s aerial power had been the key component behind widespread civilian deaths since the start of the civil war in 2011.

President Trump authorised the launchof cruise missiles in the early hours of Friday morning on a Syrian airbase thought to be behind this week’s chemical weapons attack.

Speaking to the New York Times columnist Nicholas Kristof, Clinton said she believed the US had been wrong not to have previously launched such an offensive.

She said: “Assad had an air force, and that air force is the cause of most of the civilian deaths, as we have seen over the years and as we saw again in the last few days.

“And I really believe that we should have and still should take out his airfields and prevent him from being able to use them to bomb innocent people and drop Sarin gas on them.”

The US navy launches a tomahawk land attack missile in the Mediterranean Sea.

The US navy launches a tomahawk land attack missile in the Mediterranean Sea. Photograph: Ford Williams/AP

Updated at 10.55am BST

Angelino Alfano, the Italian foreign minister, said in a statement that Italy understood the reasons behind US military action and called the strikes a “proportionate” deterrent to the further use of chemical weapons by the Assad regime.

Alfano called for a “necessary and urgent” meeting of the UN security council – where Italy, a non-permanent member, currently has a vote – and the adoption of a consensus resolution to prevent further atrocities.

He also pointed to Rex Tillerson’s upcoming visit to Moscow, suggesting that the US secretary of state could encourage Russia to use its influence in Syria and with Assad to agree “a real ceasefire, full humanitarian access and a gradual building of trust between the Syrian parties”.

Updated at 10.53am BST

Japan’s prime minister, Shinzo Abe, said he supported Donald Trump’s “resolve” against the use and proliferation of chemical weapons.

“We understand that the action taken by the United States was designed to prevent the situation [in Syria] from worsening,” Kyodo News quoted Abe as saying after a meeting of Japan’s national security council.

Abe described Tuesday’s chemical weapons attack on Syrian civilians as “extremely inhumane”, adding that he appreciated Trump’s attempts to address threats to global security, including North Korea’s nuclear and missile programmes.

Syria aside, Abe said “the threat from weapons of mass destruction is also growing more serious in east Asia”.

He added: “Japan will coordinate with the United States and the rest of the international community and play its proper role in global peace and stability.”

China’s Global Times, a nationalist Communist party-controlled tabloid that sometimes reflects official views, has published an online editorial criticising Trump’s strikes against Syria.

The newspaper said the attack was likely to spark conflict between the US and Russia and “took place despite no definitive results from the investigation by an international organisation, and was carried out in the absence of a UN security council resolution”.

“Trump’s decision to attack the Assad government is a show of force from the US president,” it added. “He wants to prove that he dares to do what Obama dared not. He wants to prove to the world that he is no ‘businessman president’ and that he will use US military force without hesitation when he considers it necessary.”

“This is Trump’s first major move in international affairs, and it leaves an impression that the decision was made in haste,” the newspaper added. “The Syrian civil war is entering a new phase. More refugees will flee the region and Europe may have to pay the price.”

A Syrian official has told the Associated Press that at least seven were killed and nine were wounded in US missile attack on airbase.

Syrian rebels on Friday welcomed a US strike on a government airbase and called for additional action, with one powerful faction saying a single strike was not enough, AFP reports.

“Hitting one airbase is not enough, there are 26 airbases that target civilians,” a key figure in the Army of Islam faction, Mohamed Alloush, said on Twitter. “The whole world should save the Syrian people from the clutches of the killer Bashar [al-Assad] and his aides.”

Other rebel groups welcomed the US strike and called for continued military action against the regime.

“The American strike against the killing tools used by Bashar al-Assad is the first step on the correct path to combating terrorism and we hope it will continue,” said Issam Raes, spokesman for the Southern Front rebel faction. “In my opinion, the message is political, and the message has arrived to Russia and been understood.”

Colonel Ahmed Osman, of the Turkey-backed Sultan Murad rebel group, said: “We welcome any action that will put an end to the regime that is committing the worst crimes in history.”

Mohamed Bayrakdar, another leader of the Army of Islam, which operates mainly around the capital Damascus, described the strike as “a bold and correct step”.

“We welcome any response to the crimes of the regime,” he told AFP.

France was among the countries informed by the US ahead of the strikes, the French foreign minister, Jean-Marc Ayrault, said.

The office of the French president, François Hollande, issued a statement confirming he had spoken with the German chancellor, Angela Merkel:

Sources have told the Guardian that US intelligence officials believe Russian personnel were at al-Shayrat airbase when sarin was loaded on to a Syrian jet. They have not established whether the Russians knew it was happening.

The base covers an area of more than 8 sq km and has two runways and dozens of buildings, silos and storage facilities.

Syrian opposition figures claim to have identified the pilot allegedly responsible for bombing Khan Sheikhun at about 6.30am on 4 April. Five hours later, close to 11.30am, a hospital treating victims from the attack was hit by a conventional bomb, dropped from a jet.

The sources say that on both occasions, a Russian Sukhoi was monitored by ground radar and aerial reconnaissance flying over the town. Flashes were picked up on the ground, indicating that ordnance had been dropped.

The air space over northern Syria is monitored heavily by Turkey, the US and Russia, and all three have precise knowledge of whose jets are in the air and where they fly.

New Zealand has joined the list of nations backing the airstrikes, with prime minister Bill English saying the US action was supported by NZ.

Russia (which, along with China, has vetoed previous UN resolutions against Assad) has called for a meeting of the UN security council to discuss the US strikes:

Russia also says it is suspending its agreement to communicate with the US over the use of Syrian airspace – possibly a reference to the so-called “deconfliction line”, via which the US military gave Russia warning on Thursday of the missile strikes (more on that here):

China, which has repeatedly blocked UN resolutions against Assad, has now issued its official response to the US strikes on Syria.

Speaking at a press conference in Beijing, the foreign ministry spokeswoman, Hua Chunying, stopped short of explicitly condemning the US airstrikes but said China had always been opposed to the “use of force”.

Hua said China also opposed “the use of chemical weapons by any country, organisation or individual, in any circumstance and for any purpose”.

There was now an urgent need to prevent a “further deterioration” of the situation in Syria, Hua added.

With the UK, Australia, Israel, Turkey, Saudi Arabia and Japan offering strong backing for the US strikes, Indonesia has given a more cautious response.